System for vapor deposition of thin films

ABSTRACT

The disclosed invention comprises a method of vapor depositing a substantially uniform thin film of a photoconductive material on a substrate body, and comprises positioning a plurality of substrate bodies on a plurality of elongated horizontal extending cylindrical mandrels; rotating each of said mandrels about an associated longitudinal axis thereof while simultaneously transporting the mandrels in an annular path about a horizontal axis. Vapor deposition is carried out under vacuum using a photoconductive material which is positioned in a planar array of crucibles which is located within the annular path of travel of the mandrels.

United States Patent 1 Erhart et al.

1 1 SYSTEM FOR VAPOR DEPOSITION OF THIN FILMS [75] Inventors: Francis J. Erhart, Webster; Harold H. Schroeder, Rochester, both of NY.

[73] Assignee: Xerox Corporation, Stamford.

Conn.

221 Filed: Nov.23, 1973 [21] App]. No,:418,510

Related US. Application Data [63] Continuation-impart of Scr. No. 24 1374, April 17,

1972, abandoned [521 US. Cl. .1 427/39; 427/74; 427/124; 427/76; 118/491 [51} Int. Cl. C23C 11/00 [58] Field ofSearch ..117/]O6 107.1,93.l; 1 18/49. 1 48 [56] References Cited UNITED STATES PATENTS 2,501 563 3/1950 Colbert et a1 117/911 1 Oct. 7, 1975 3.068510 12/1962 Coleman 4. 117/911 3.417.733 12/1968 Makino i. ll7/lU7.l 3,622,712 11/1971 Moore et a1, .1 117/106 Primary ExaminerWilliam E. Schulz [57 1 ABSTRACT 9 Claims. 13 Drawing Figures U.S. Patent 061. 7,1975 Sheet 1 0f 10 3,911,162

US. Patent 0a. 7,1975 Sheet 2 0f 10 3,911,162

US. Patent Oct. 7,1975 Sheet 3 0f 10 3,911,162

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US. Patent 061. 7,1975 shw4 0f10 3,911,162

ln ukwl I! 11 I III U.S. Patent 0a. 7,1975 Sheet 5 of 10 3,911,162

U.S. Patent Oct. 7,1975 Sheet 7 0f10 3,911,162

US. Patent Oct. 7,1975 Sheet80f 10 3,911,162

WNW Qlull lmllll 2/4? U.S. Patent Oct. 7,1975 Sheet 9 0f 10 3,911,162

US. Patent 0a. 7,1975 Sheet 10 of 10 3,911,162

226' ZZZ SYSTEM FOR VAPOR DEPOSITION OF THIN FILMS This is a continuation-inpart of application Ser. No. 244,374, filed Apr. 17, 1972, now abandoned.

This invention relates to an improved method and apparatus for the vapor deposition of a relatively thin film on a substrate body. The invention relates more particularly to an improved method and apparatus for fabricating an electrostatographic plate by the vapor deposition of a photoconductive material on a substrate body.

In one form of electrostatographic reproduction system. a latent electrostatic image is formed on an image retention surface and is developed by contacting the surface with a developer material which generally comprises a pigmented. clectroscopic, thermoplastic resinv Attractive electrostatic forces cause the developer material to adhere to the latent electrostatic image in image configuration. The latent image is subsequently transferred to a record medium such a sheet or web of paper to which it is fixed.

An image retention surface in this type of electrostatographic reproduction system generally comprises a relatively thin film of photoconductor material such selenium or alloys thereof which is deposited on an electrically conductive. substrate body. The film preferably has a thickness of about 55 to 60 microns. The substrate body is fabricated of a metal which is formed as a drum or alternatively as a flexible endless belt. Generally, an interface is formed on the substrate body prior to deposition of thc photoconductor material on the substrate body. The interface which is formed on the electrically conductive substrate body functions to provide an electrically resistive barrier between the photoconductor layer and the substrate. During image reproduction, a uniform clectrostatographic charge is initially formed on the photoconductor surface. The surface is then exposed to activating electromagnetic radiation in image configuration such as is provided by exposure to a light source through a phototransparency. The photoconductor material automatically alters the charge on its surface in those areas which have been exposed to activating electromagnetic radiation.

The quality ofa reproduced image in an electrostatographic reproduction system of this type is dependent in part on the characteristics of the deposited photoconductor film. This film should be substantially uniform in thickness and should exhibit uniform photoelectrical characteristics across its surface. Additionally, in order to provide uniformity of image reproduction in different electrostatographic machines, these film char acteristics should be substantially uniform over all such image retention surfaces.

A photoconductor film has heretofore been formed on an electrically conductive substrate body by the vaporization and deposition of the photoconductor material on the substrate in an evacuated atmosphere. The substrate body is initially cleaned and is then surface treated or coated to establish the interface barrier thereon. Interface surface treatment is accomplished by coating or alternatively by heating the body when the body is formed of materials such as aluminum. The vaporization deposition, and adherence of the photoconductor material to the substrate is best effected when the substrate body is brought to an elevated temperature. This process has been practiced in the past by supporting a substrate on an elongated mandrel and by rotating the mandrel about an axis thereof which extends in a horizontal plane. Heating of the substrate body was accomplished by conveying a heated liquid to the mandrel or alternatively by establishing a glow discharge between an electrode and the substrate body. The mandrel is positioned adjacent an open crucible which extends coextensively with the length of the mandrel and contains a photoconductor material. This arrangement, while operative to produce useful image retention surfaces, is limited in that the image retention surfaces thus produced exhibit variations in the characteristics of the deposited film which in great part relate to the characteristics of the associated crucible. Furthermore, these techniques do not readily lend themselves to a relatively economic and high rate of production.

Accordingly. it is an object of this invention to pro vide an improved method and apparatus for vapor depositing a relatively thin film of photoconductor material on a substrate bodyv Another object of the invention is to provide an improved method and apparatus for producing an electrostatographic image retention surface in a relatively economic manner and at a relatively high rate of production.

Another object of the invention is to provide an im proved method and apparatus for producing an electrostatographic image retention surface by vapor deposition in an evacuated chamber and which eliminates the need for a preliminary formation of an interface surface on the substrate body.

Another object of the invention is to provide an improved mcthod and apparatus for the production and of an electrostatographic image retention surface which effects relatively efficient use of the photoconductor material.

Another object of the invention is to provide an improved method and apparatus for producing clectro statographic image retention surfaces which exhibit an improved uniformity in the thickness of the deposited film.

Another object of the invention is to provide an improved method and apparatus for producing electrostatographic image retention surfaces which exhibit improved uniformity in the electrical characteristics of a deposited film.

In accordance with features of the method of this invention, a plurality of elongated horizontally orientated mandrels each supporting thereon a plurality of substrate bodies are each rotated about a horizontally orientated longitudinal axis thereof and are transported in a vertically orientated path about a planar array of erucibles containing photoconductor material. The photoconductor material is heated to a temperature for providing vaporization and deposition of the material upon the substrate bodies.

ln accordance with another feature of the method of this invention, an electric discharge is established between an electrode and the substrate bodies for forming an interface on said bodies and for preheating said bodies to a desired temperature suitable for vapor de position.

ln accordance with other features of this invention, an apparatus for depositing a relatively thin film on a substrate body comprises a vacuum chamber, a verti cally orientated mandrel support plate which is rotatably mounted about a horizontal axis, a plurality of elongated, horizontal extending, rotatably mounted mandrels arrayed on the mandrel support body and rotated therewith about a planar array of crucibles. Means are provided for rotating the mandrel support body about its horizontal axis while simultaneously rotating each of the mandrels about a longitudinal axis of the mandrel. The mandrels are each adapted for receiving and supporting a plurality of substrate bodies upon which a photoreceptor film is to be vapor deposited. In accordance with other features of the apparatus of this invention, the vacuum chamber comprises a vertically positioned wall member and a bell shaped member adapted to be transported into union with the wall member and to form a vacuum tight enclosure therewith. The bell shaped vacuum member encloses the rotatable mandrel support body and the mandrels mounted thereon. The planar array of crucibles are supported fron an inner wall surface of the bell shaped vacuum chamber member and are positioned within a path of travel defined by rotation of the mandrels.

With the apparatus and method of this invention, clectrostatographic image retention surfaces are produced at relatively high rates and in a relatively economic manner with improved physical and electrical characteristics. Additionally, the processing of the substrate body is enhanced and an improved interface is established by simultaneously heating and forming the interface immediately prior to vapor deposition. These and other objects and features of the invention will become apparent with reference to the following specifcation and to the drawings wherein:

FIG. I is a side elevation view of an apparatus constructed in accordance with features of this invention for the vapor deposition of a thin film on a substrate body;

FIG. 2 is a view taken along lilies 2 2 of FIG. I;

FIG. 3 is a view taken along lines 33 of FIG. 2;

FIGS. 4A and 4B are side clevational views of portions of an alternative embodiment of an apparatus constructed in accordance with features of this invention for the vapor deposition of a thin film on a substrate body;

FIG. 5 is a view taken along lines 55 of FIG. 4A;

FIG. 6 is a view, partly broken away, taken along lines 66 of FIG. 4B;

FIG. 7 is an enlarged side view, partly broken away. of a portion of the apparatus of FIG. 48;

FIG 8 is an enlarged view, partly broken away, of a portion of the apparatus of FIG. 6',

FIG. 9 is a plan view of a planar array of crucibles employed with the apparatus of this invention;

FIG. 10 is a view of a portion of the vacuum chamber employed with the apparatus of FIGS. 1 and 4 and illus trating a crucible power supplying means, a glow discharge power supplying means, a glow discharge power supply means and temperature sensing and control equipment for the apparatus;

FIG. II is a plan view of the crucible array of FIG. 9 illustrating the flow paths of crucible heating current therein; and,

FIG. 12 is a cross-sectional view of an arrangement for vapor depositing a film on a planar substrate body.

Referring now to the drawings, and more particularly to the embodiment of the apparatus of this invention shown in FIGS. 1, 2 and 3, there is illustrated a vacuum chamber 18 having a vertically orientated wall member 20 which is secured in a stationary position by welding,

for example. to the vertical beam or wall body 22. The chamber enclosure further includes a generally bellshaped housing 24 having a vacuum flange member 26 mounted thereto. Electrical operating power is derived from the sources 220, 232 and 518 (FIG. IO) and is coupled through this flange to various components within the vacuum chamber. The vacuum chamber formed by the bell shaped member 24 and the vertically orientated wall member 20 comprises a relatively large size chamber adapted for the mass production of image retention surfaces. The chamber typically has dimensions on the order of about 6 to 8 feet in diameter and 10 to 20 feet in length. It is constructed in accor dance with conventional vacuum techniques for reducing the pressure within the chamber to values on the order of about I X IO" to l X 10* Torr. A pumping means, not illustrated, for pumping down the chamber to these levels comprises a conventional vacuum system which includes a roughing pump, diffusion pumps and mechanical blowers.

A plurality of clectrostatographic image retention surface substrate bodies are positioned within the chamber 18 for vapor deposition of a photoconductor on the surfaces thereof. As indicated in greater detail hereinafter. these substrate bodies are supported on ro tatable mandrels within the chamber. In order to facilitate the placement and the mounting of the substrate bodies within the chamber and in order to enhance the removal ofthese bodies subsequent to film deposition. the bell shaped vacuum chamber member 24 is adapted to be withdrawn from union with the wall member 20 for a distance sufficient for mounting and demounting of the substrate bodies on the mandrels. The bell shaped member 24 is formed, for example, of relatively heavy metal plate. in order to render it transportable in a longitudinal direction. the chamber member 24 is supported by a frame 28 to which are mounted roller guides or wheels 30 which are aligned with and guided along a track 32. A drive means, not illustrated, is provided and is coupled to the frame 28 for effecting motion of the frame and the supported member 24 along the track 32 for a distance sufficient for providing access to the free end of the mandrels which are then exposed by the displacement of this chamber member.

A plurality of substrate bodies 40, 42, 44 and 46 are mounted on an elongated rotatable mandrel 48 which is adapted for rotation about its longitudinal axis 49. Additional rotatably mounted mandrels 50, 52, 54, 56 and 58 each having a plurality of substrate bodies mounted thereon are also provided. While six such mandrels each having four substrate bodies mounted thereon are illustrated in the drawings, it will be appreciatcd from the discussion herein that the number of mandrels and the number of substrate bodies which can be accommodated for vapor deposition can be varied.

The substrate bodies illustrated in FIGS. I through 3 are shown to comprise in one embodiment relatively thin. flexible, electrically conductive, seamless, endless belts formed, for example. of nickel, brass, aluminum or stainless steel. These bclts typically have a thickness on the order of about 3 to 10 mils. In FIG. 3, an endless belt 59 is shown supported by a pair of plastic, gener ally discshapcd support form members 60 and 62 which are positioned back to back and are secured together by means, not illustrated, in order to form a configuration which is adapted for supporting the endless belt 59. The forms 60 and 62 each include apertures formed centrally therein and through which the mandrel 54 extends. A key means, not illustrated, secures this form assembly to the shaft 54 for rotation therewith. Longitudinal movement of the form assembly and its supported belts is restricted by a collar 64 which is secured to the shaft 54. An annular shaped coating mask 66 having an inwardly extending rib 68 is positioned on a surface of the inner belt. A similar mask 70 is positioned intermediate the belt 59 and an adjacent belt 72. These masks function to define edges of the areas of deposited photoconductor material on the belts, to space the belts on the mandrels, and to reduce generally the deposition of photoconductive material upon the mandrel. While FIGS. 1-3 illustrate the positioning of cylindrical shaped substrate belts in the chamber for the vapor deposition of a photoconductor material thereon, substrate support bodies comprising cylindrically shaped drums may equally well be positioned on the mandrels.

In addition to the cylindrical configuration thus far described, the substrate bodies can assume other configurations, as for example, a planar configuration as is illustrated in FIG. 12. The substrate bodies 51, 53, 55 and 57 of FIG. 12 are secured to surfaces of a support form 61 by clamps or hold downs, not illustrated. The support form is frame shaped and includes spokes 63 extending from these surfaces to a hub 65. The hub is positioned on and keyed to a mandrel 67 for rotation therewith.

A relatively efficient utilization of coating material, and enhanced randomization of photoeonductor deposition on the support substrates, and an improved control of deposited film thickness is effected by providing a planetary rotational motion of the type wherein each of the mandrels is rotated about its horizontally extending longitudinal axis while the rotating mandrels are transported in a path extending in a substantially vertical plane. This desired cpicyclic motion is effected by the provision of a rotary support body referenced generally as 73 which is formed by an annular shaped disc 74 having a plurality of radially extending arm segments 7888 (FIG. 2) mounted thereto, such as by welding. each of which supports hubs 90-100 respectively at a distal segment thereof. The arm segments are spaced apart and braced by struts 102-112 which ex tend between adjacent arm members near the distal lo cated hub segments. Inner spacing and bracing struts 114-124 are positioned adjacent the plate 74 and are welded to the plate and to adjacent radial arm members. The plate 74 includes a centrally located aperture 123 (FIG. 3) formed therein and into which a hub 124 extends. The hub 124 which is welded to the plate 74 is a member of a hollow rotary drive shaft which further includes a heavy walled tubular member 126, a tubular shaft segment 128, a circular shaped plate 130, and a circular plate 132. These members are secured together by welding. The tubular drive member 128 extends through the vertically orientated vacuum chamber wall member and through the backing wall or beam 22. There is mounted to an outer surface of the shaft 128 a pulley 134 which is engaged by a drive belt 136. A primary source of rotary motion comprising an electric motor 138 is provided and a drive pulley 139 is mounted on a drive shaft 140 of the motor. The drive shaft 140 causes rotation of the plate 74 and results in the transport of hubs 90-100 in an annular, and more particularly a circular, path extending in a vertical plane within the chamber.

As indicated hereinbefore, each of the substrate body support mandrels 48-58 is rotated about its horizontally orientated longitudinal axis. The mandrels are each rotatably supported and driven at one end thereof while an opposite end of the mandrel provides for mounting of the substrate support forms and belts thereon. FIG. 3 illustrates one end of the mandrel 54 extending through the hub 96. Roller bearings and 152 are press fitted near end segments of a sleeve 154 which is fitted into a cylindrical bore in the hub 96. The mandrel 54 is thus rotatably mounted. A bevel gear 156 is mounted on the mandrel and is driven in order to impart rotary motion about a horizontally orientated, longitudinal axis of the mandrel. A rotary force for rotating the mandrel 54 is derived from a main bevel gear 158 and is coupled to the mandrel gear 156 through a bevel gear 160, a drive shaft 162 which is journaled in a body 164 and a bevel gear 166. The body 164 is welded to the rotary plate 74. Each of the spindles in the apparatus are similarly rotatably supported and dcrive rotation forces from the main bevel gear 158.

Rotary motion is imparted to the main bevel gear 158 independently of the rotary motion of the plate 74 by a drive shaft which is concentrically positioned with respect to the tubular shaped rotary drive means which rotates the plate 74. The main bevel gear 158 is secured to the drive shaft 170 for rotation therewith. The shaft 170 is journaled within the tubular member 128 and extends through bearings 172, 174 and through the hub 124. A drive pulley 176 is mounted on the drive shaft and is driven by a belt 178 from an electric motor source 179 (FIG. 2). Thus, rotation of the drive shafts 128 and 170 result in a cpicyclic motion of the substrate bodies. It is noted that the mandrels and the main support plate 74 are independently driven and their rates of rotation can advantageously be independently varied.

During the vapor deposition process. it is desirable to monitor the temperature of the substrate bodies. A thermocouple pickup junction 180 is secured by spring loading means, not shown, to an under surface of the substrate body 59. Thermocouple leads 182 and 184 extend from thejunction 180, and fed through the sub strate support body, through an aperture 186 in the tubular mandrel 54 and are dressed along an inner surface of the mandrel and are electrically coupled to slip rings 188 and 190 which are mounted on the mandrel shaft. Pickup brushes 192 and 194 are mounted in, and. are insulated from the sleeve 154 and leads extending therefrom are dressed through an aperture 196 in the sleeve 154 and through the hub 196 and are led to a thermal indicator and recorder, not illustrated.

A means for supporting a photoconductor material within the chamber 18 and for vaporizing the material comprises a planar array 200 of crucibles (FIG. 1) which are located within the vacuum chamber 18 and which are positioned within an annular path defined by the travel of the support mandrels. This planar array of crucibles is supported from an end segment 202 of the bell shaped housing member 24 and is transportable therewith. Thus, when the bell shaped housing 24 is separated from the wall member 20 the planar array of crucibles is similarly withdrawn. As the bell shaped member 20 is advanced toward and is closed upon the wall member 20, the planar array is thereby automatically positioned within the annular path defined by the cpicyclic motion of the mandrels. An arrangement of the planar array of crucibles is described in greater dc tail hereinafter with respect to the embodiment of the apparatus disclosed in FIG. 4. For the present, it is noted that in the apparatus illustrated in FIGS. l3, the array 200 includes flanged support segments 204 and 206 which are mounted on a plate 208. The plate 2(l8 is in turn supported on cross members 210 and 2]] which are secured to a support beam assembly 2l4. The beam assembly 214 is mounted to a plate 216 which in turn is supported from the chamber wall segment 202. A support brace 220 extends between the beam assembly 214 and the plate 216. Although the array 200 of crucibles is shown to be centrally located within a circular path of travel of the mandrels. the array can be positioned at locations displaced from this central location. The crucible assembly can alternatively be located outside the annular path defined by the travel of the mandrels.

Prior to closure of the vacuum chamber, each of the plurality of boat shaped crucibles 222 in the array 200 have deposited therein a predetermined amount of photoconductor material which is to be deposited on the substrate bodies. The photoconductor material comprises for example selenium or alloys thereof.

Current conducting leads 224 and 226 extend from the chamber through feed through connections (FIG. 10) and are coupled to a crucible transformer 228 to which a voltage is applied from a line source 220 under the control of a temperature servo control means 232. The servo control 232 receives monitoring temperature information from one or more temperature sensors, not shown. such as thermocouples attached to the crucible array. The crucibles are made of a conductive material such as stainless steel and current flows therein thereby heating and crucible assembly 200 and causing the as sembly to heat both the substrate support bodies which are transported within the chamber and the photoreceptor material. The temperature of the substrate bodies. which have a relatively low thermal mass and are supported by plastic forms having a relatively low thermal conductivity is increased to the desired coating temperature. The photoconductor material is heated to vaporization and deposits upon the surfaces of the support body substrate. Thus, the crucible assembly in addition to containing the photoconductor material and causing its vaporization further operates to heat the substrate support body to a desired temperature for satisfactory vapor deposition of the photoconductor material on the surface of the substrate.

Photoconductor alloys suitable for use with the present invention include. without limitation. selenium al loyed with arsenic. tellurium, thallium, antimony, bis muth and mixtures thereof. U.S Pat. Nos. 2,803,542; 2,822.300; 2,745.327; 2,803,54l; 2,970,906; and 3.3 l2,548 illustrate in more detail suitable applications and process techniques for selenium and selenium alloys which may be used in carrying out the process or in using the apparatus of the instant invention. A particularly preferred photoconductivc alloy suitable for use in the instant invention comprises selenium alloyed with arsenic in the range of from about U. l to 50 weight percent. US. Pat. Nos. 2,803,542; 2,822,300 and 3.311548 more fully define such alloys and are incorporated herein by reference. Generally, when selenium is alloyed with arsenic. the vapor deposited photocon- (ill ductive layers of such alloys exhibit an inherent fractionation which is characterized by a composition gradient in which greater concentrations of arsenic are found at the free surface of the alloy layer with the concentration of the arsenic decreasing towards the photoconductor-substrate interface. In using the pro' cess and apparatus of the instant invention, it has been observed that for very low arsenic concentrations (i.e., (l. l- 0.75 wt)? As balance selenium), that a relatively flat concentration gradient for the arsenic results. A flat concentration gradient is preferred in that it provides excellent reproducibility in the composition of the arsenic-selenium layer from one production run to another; and further, provides better control of the electrical characteristics of the photoconductivc layer.

In a typical coating operation, the substrate support bodies each comprise an electroformed, flexible, endless belt which if formed of nickel and which has a thickness of about 4.5 mils, a diameter of about 20 inches and a width of about 16 /2 inches. The substrate support bodies are cleaned and an organic interface, for example, is formed thereon by coating. The belts are initially mounted on the support forms which are fabricated of a material which offers sufficient support for preventing physical damage to the relatively delicate thin walled substrate, provides a thermal barrier for reducing the transfer of heat between and sup ort and the substrate and is compatible with the vacuum process. Suitable materials from which these forms are fabricated comprise polypropolene and polystyrene. The coating masks which can be fabricated of plastic or metal are positioned on an edge of a form and the form is then mounted on the mandrel shaft. A plurality of such assemblies are mounted on the mandrel until the mandrel is loaded to capacity. A photoconductor material which comprises for example an alloy of selenium and arsenic is deposited in the individual boat shaped crucible members. It is noted that the loading process is greatly facilitated since the bell shaped memher 24 which is withdrawn from the wall 20 and beyond the distal end segments of the mandrels provides ready access for the operator in performing the mounting operation. Further, the removal of the boat array from that area within the path traveled by the mandrels during the coating operation facilitates charging of the boats. The bell shaped member 24 is then closed upon the wall member 20 and the planetary motion of the mandrels is initiated by energizing the motors I38 and [FIG 2].Typically. the tubular shaft assembly and the plate 124 mounted therefrom rotates at a rate of about 5 RPM. and the mandrels rotate at a rate of about 15 RPM. The vacuum pumping means is then activated and pump down proceeds until a pressure on the order of about 5 X 10 Torr is attained. Crucible power is then applied to the crucible assembly from the transformer 228 (FIG. 10) under the control of a time temperature control means 232. Prior to heating of the crucible assembly, the substrate bodies are at a temperature of about 25C The temperature control means 232 is adapted to increase the temperature of the crucible and of the substrate bodies in accordance with a predetermined temperature program. This means in cludes a closed loop control system which derives tem perature indications from sensors located within the chamber. Temperature control and programming means of this type are well known in the art. During dcposition, the temperature of the substrate bodies rises to a value within a range of about 7085C. At this temperature, an acceptable photoconductor film is deposited which exhibits both desirable physical and electrical characteristics. The crucible will be maintained at the programmed temperature until the proper thickness of photoconductor material has been vapor deposited upon the substrate body. This is controlled by the amount of photoconductor material deposited in the crucibles, the time-temperature program provided by the control means, and the pressure within the chamber. When the proper thickness has been attained, crucible power is decoupled, the crucibles are cooled, and the chamber is then returned to atmospheric pressure.

In a typical operation, the cycle of events will include a vacuum pumping interval of about 9.5 minutes, a crucible heating interval of about 40 minutes, a dwell time of about 6 minutes during which time the temperature of components within the chamber decreases, and f1- nally a depressurization interval of about 6 minutes during which the chamber is returned to atmospheric pressure.

The apparatus and method described herein advantageously provides for the simultaneous coating of a relatively large number of substrate bodies thereby providing a relatively efficient, economic, and high production capacity system. In addition, the planetary motion of the substrate bodies within the vacuum coating chamber requires substantially less coating material than prior techniques for an equivalent thickness. A relatively high degree of randomization of deposition occurs which enhances its uniformity of coating between different substrate support bodies. Quality control of the produced eleetrostatographic image retention surfaces is thereby greatly enhanced. For example, a photoconductor thickness measurement need only be taken on a deposited film associated with a single mandrel and this effectively measures the entire batch of photoreceptors. Not only is the uniformity of photoreceptor production enhanced but the labor involved in quality control of the photoreceptor is thereby reduced. Additionally, control of photoconductor thickness within a particular photoreceptor is more precise than prior arrangements. In addition to the advantageous uniform thickness of the characteristics attending the randomization provided by planetary coating, improved electrical characteristics of the photoreceptor are also realized in that the uniformity of electrical properties between different coatings is enhanced.

An alternative embodiment of an apparatus constructed in accordance with features of this invention is illustrated in FIGS. 4-11. Those elements of FIGS. 4-11 which perform functions similar to those performed by elements of FIGS. 1-3 bear the same reference numerals. In the embodiment of FIGS. 411, a plurality of mandrels 400, each of which are horizontally orientated are rotatably supported at one end thereof by a plate 402 (FIG. 4A). This plate is mounted on a drive shaft 404 and is journaled through the vertical wall plate and its support beam 22 to a pulley 406 which is secured to an end of the shaft. The pulley is coupled via a drive belt 408 to a drive pulley 410 which is mounted on a drive shaft ofa motor 412. Excitation of the motor 412 causes rotation of the drive pulley and a corresponding rotation of the plate 402. A ring shaped body 414 having a plurality of hubs 416 formed therein is mounted to and secured to the plate 402 for rotation therewith. The hubs. which are positioned in an annular array, each include a horizontally extending cylindrical bore 417 which functions as a journal for the mandrels 400 extending therethrough. A relativeiy large diameter spur gear 418 having gear teeth 419 formed on its peripheral surface is journaled about a segment 420 of the drive shaft 404. Longitudinal motion of the gear 18 is restricted by a drive shaft segment 422 of enlarged diameter and a collar 423. The gear 418 is therefore free to rotate independently of the rotation of the plate 402. The spur gear 418 in cludes an integral hub segment 423 having gear teeth 421 formed about a peripheral surface of the hub 423. The hub 423 is engaged and driven by a spur drive gear 424 which is mounted on a shaft 426. The shaft 426 which in FIG. 4A is shown by dashed lines extends through the vacuum chamber wall member 20 and the backup beam 22 and includes a pulley, not illustrated, mounted on an outer segment thereof which is driven by an electric motor 425 (FIG. 5). Each of the mandrels 400, which extend through a cylindrical bore 417 in the ring 414, has mounted to an end thereof a spur gear 428 which engages the gear teeth 419 of the gear 418. The plate 402 and the plurality of mandrels 400 are thus independently rotatable thereby advanta geously providing means for independently altering their speeds of rotation.

The planar array 200 of crucible members which was referred to hereinbefore is formed by a plurality of boat shaped crucible members 222 (FIGS. 9 and 11 Each of these members includes flanged end segments 449 (FIG. 7) which are welded or bolted to the flanges of other members in order to form a plurality of crucible strips 450-467 (FIG. 11). The strips 450-459 extend substantially coextensively with the mandrels 400 while relatively shorter outrigger crucible strips 460-467 are provided and are positioned near ends of the array for assuring distribution of vaporized photoconductor material near opposite end portions of the vacuum cham ber. The crucible members 222 are typically fabricated of stainless steel. Each of the crucible strips are supported above an associated longitudinally extending strip 208 by flange members 209 (FIG. 7) which are lo cated along the length of a crucible strip. In addition, ceramic insulating spacers 468-471 are provided and are mounted to a flange 206 and a support block 207 at opposite ends of each strip for providing electrically insulated support and electrical terminations for the crucible strips. The strips 208 are mounted to a support strip 211 which extends in a direction normal to the strip and is secured to the beam 214. The beam 214 which comprises a rectangular shaped channel is welded to a plate 215 which in turn is mounted to a plate 216. The plate 216 is supported from an extending mount 218 wich is secured to an inner wall segment 202 of the vacuum chamber member 24. A brace 220 extends between the beam 214 and the plate 215 for providing additional support for the beam 214.

Heating current is applied to the planar array 200 of crucibles from the crucible transformer 228 (FIG. 10) under the control of the servo temperature control means 232. Current flows from this transformer via vacuum feed-throughs to the outrigger strips 464 and 467 of the planar array (FIG. 11). Adjacent crucible strips are strapped together by relatively heavy, flexible, conductive webbing 484 as best illustrated in FIGS. 6 and 8 in order to provide a series current flow path through the crucible strips of the array. The strapping In addition to the advantages enumerated above, the outrigger configuration increases the efficiency of the system with respect to the amount of photoconductive material used in each batch operation. This is proven by the fact that if the outrigger configuration were not used, in order to obtain uniformity of photoeonductor coating thickness, the entire crucible array would have to be extended well beyond both ends of the mandrel assembly. This would, of course, result in a much greater amount of photoeonductor material being evaporated during each batch operation.

In operation, the bell shaped chamber 24 (FIG. 4B) is withdrawn from union with the wall member 20 (FIG. 4A). The chamber member 24 is withdrawn beyond the distal segments 600 of the mandrels 400 for providing access for mounting a pluraltiy of tubular shaped substrate bodies 602 on each of the mandrels. A plurality of edging masks 604 are provided and positioned between the substrate members on a mandrel in order to define an edge for the deposited coating. In a typical example, the substrate body 602 comprises a tubular body formed of aluminum and has a nominal diameter of about 3V2 inches, a length of about 16 inches, and a wall thickness of about three-sixteenths of an inch. It is noted that the substrate bodies need only have been previously cleaned before mounting on the mandrels. The boats of the crucible array are charged with a photoeonductor material, referred to in detail hereinbefore. The bell shaped housing member 24 is then advanced into contact with the wall member 20 in order to provide a vacuum tight seal. The electric motors are energized in order to rotate shafts 404 and 426 and to initiate the planetary motion of the sub strate bodies within the chamber. A vacuum pumping operation is initiated by activating the vacuum pumping means. In a typical example, the plate 402 is rotated at a rate of about RPM and the mandrels 400 are rotated at a rate of about RPM. Pump down of the chamber proceeds until the chamber pressure has reached a value on the order of 10 to 50 milliTorr. This chamber pressure, when established, is maintained by a pressure sensing transducer which operates in conjunction with the vacuum pumping mcans. A gas is ad mitted to the chamber by a control leak during this period of time. The gas can comprise air which has been conveyed through a moisture removing device. Other gases such as oxygen may also be employed. With the chamber pressure maintained within the desired range, the glow discharge process is initiated. A voltage of between 1000 and 5000 volts is applied to the electrode elements which establishes a high voltage plasma between the glow bar cathodes and the substrate body anodes. This plasma discharge preheats the substrates prior to initiation of the vapor deposition of the photoeonductor material on the substrates. Additionally. the plasma discharge functions to establish an interface on the aluminum substrate by forming a thin aluminum oxide film on the outer surfaces of these bodies. The plasma discharge continues until a substrate temperature on the order of about C. to about 75C. is at tained. The control leak is shut off and pump down is again initiated in order to reduce the pressure within the chamber to a pressure on the order of about 5 X 10 Torr or less. Electrical power is then applied to the crucible assembly for heating the crucibles and causing vaporization of the photoeonductor material contained therein. The closed loop temperature control means 232 provides for controlling the temperature of the crucible in a programmed manner. Power is applied to the crucible from the alternating power source 220 through the transformer 228 under the control of temperature programm control means 232. The substrate temperature then generally exhibits an increase in temperature of about 10C. to l5C. during the application of power to the crucible assembly. Power will be applied under program control until the desired alloy thickness is established. At this time, power to the crucible assemblies is interrupted and a cooling dwell time is provided. The vacuum chamber is then returned to atmospheric conditions.

In a typical cycle of events. the initial evacuating operation is performed in 12 minutes; the glow discharge is performed in 10 to minutes, the further reduction in vacuum within the chamber occurs in about l minute; the power is applied to the crucibles for between about 25 to minutes; the temperature cooling dwell time is about 5 minutes; and the pressurization to atmospheric pressure occupies approximately 5 minutes.

The embodiment of this invention described with respcct to FIGS. 4-11 is particularly advantageous in that it eliminates the need for the preliminary formation of an interface on the substrate bodies. In addition to eliminating this step, the interface formed by this method provides improved characteristics in the photo receptor since the interface is formed under evacuated conditions immediately prior to deposition of the pho toconductor material and further handling and exposure at atmospheric conditions is avoided.

There has thus been described an improved method and apparatus for fabricating an electrostatographic image retention surface by the vacuum depositon of a photoeonductor material on a substrate support body. The method and apparatus provides for the cpicyclic motion ofa plurality of substrate bodies which are horizontally orientated on a rotating mandrel. A plurality of such mandrels are provided and a relatively large number of substrate bodies are thereby rotated while they are simultaneously coated by the evaporation and deposition of the photoeonductor material. Addition ally, a glow discharge means is provided which establishes an interface on the substrate body. which preheats the body to operating temperatures prior to vac uum deposition. or which both forms the interface and preheats the body. The described method and apparatus are advantageous in that an improved distribution of photoeonductor material is provided for a useful range of film thicknesses; a more efficient use of the photoeonductor alloy is effected; an enhanced randomization of deposition takes place thereby resulting in an improved film thickness control; the intermediate step of chemically treating a substrate body for establishing an interface is avoided and an enhanced photoeonductor film results therefrom; and, mounting and demounting of a relatively large number of substrate support bodies on the mandrels is provided thereby resulting in an increased economical use of production equipment and an increased rate of production of clectrostatographic image retention surfaces.

While there has been described a particular process and apparatus for carrying out the invention, it will be understood that various modifications may be made thereto without departing from the spirit of the inven tion and the scope of the appended claims.

What is claimed is:

1. A method of vapor depositing a substantially uniform thin film of photoconductive material on a substrate body comprising the steps of:

positioning a plurality of substrate bodies on a plurality of elongated. horizontally extending cylindrical support mandrels;

rotating each oisaid mandrcls about an associated longitudinal axis thereof and simultaneously trans porting said plurality of mandrels in an annular path about a horizontal axis;

establishing an evacuated atmosphere about said mandrels; and

vaporizing a suitable photoeonductor material, which is positioned in a planar array of crucibles located within the annular path of travel of said mandrels. with at least one additional crucible being positioned in an outrigger configuration at each corner of the planar array said crucible array extending substantially coextensively along the entire length of the plurality of substate bodies.

2. The method ofclaim l in which the substrate bod ies are heated to an elevated temperature prior to vapor deposition.

3. The method of claim 2 wherein said substrate bodies are heated by establishing an electrical discharge near said support bodies,

4. The method of claim 1 including the step of forming an interface barrier on said substrate bodies prior to the raising of said bodies to an elevated temperature.

5. The method of claim 4 including the step of establishing a glow discharge near said substrate bodies for forming an interface barrier on the surface of said bodies and for preheating said bodies prior to deposition of said material thereonv 6. The method of claim 1 in which the crucibles are located outside the annular path of travel of the mandrelsv 7. The method of claim 1 in which the photoeondue tor comprises a material selected from the group consisting of vitreous selenium and vitreous selenium alloys.

8. The method of claim 1 in which the material which is vapor deposited comprises a vitreous alloy of selenium and arsenic 9. The method of claim 1 in which the material which is vapor deposited comprises vitreous selenium alloyed with a material selected from the group consisting of arsenic, tellurium, thallium, antimony, bismuth and mixtures thereof.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION DATED October 7, 1975 INVENTOR(S) 1 Francis J. Erhart and Harold H. Schroeder It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3 line 18, delete "fron" and insert from.

Column 10. line 54, delete "wich" and insert whic Column 11, line 39 delete "assenblies" and insert -assemblies-.

Column 12 line 26, delete "assenblies and insert assemblies-.

Column 13 line 40, delete "milliTorr" and insert milli Torr-.

Column 14, line a. delete "programm" and insert program-.

Signed and Scaled this seventeenth Day of February 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'lalenrs and Trademarks 

1. A METHOD OF VAPOR DEPOSITING A SUBSTANTIALLY UNIFORM THIN FILM OF PHOTOCONDUCTIVE MATERIAL ON A SUBSTRATE BODY COMPRISING THE STEPS OF: POSITIONING A PLURALITY OF SUBSTRATE BODIES ON A PLURALITY OF ELONGATED, HORIZONTALLY EXTENDING CYLINDRICAL SUPPORT MANDRELS, ROTATING EACH OF SAID MANDRELS ABOUT AN ASSOCIATED LONGITUDINAL AXIS THEREOF AND SIMULTANEOUSLY TRANSPORTING SAID PLURALITY OF MANDRELS IN AN ANNULAR PATH ABOUT A HORIZON TAL AXIS: ESTABLISHING AN EVACUATED ATMOSPHERE ABOUT SAID MANDRELS, AND VAPORIZING A SUITABLE PHOTOCONDUCTOR MATERIAL, WHICH IS POSITIONED IN A PLANAR ARRAY OF CRUCIBLES LOCATED WITHIN THE ANNULAR PATH OF TRAVEL OF SAID MANDRELS, WITH AT LEAST ONE ADDITIONAL CRUCIBLE BEING POSITIONED IN AN OUTRIGGER CONFIGURATION AT EACH CORNER OF THE PLANAR ARRAY, SAID CRUCIBLE ARRAY EXTENDING SUBSTANTIALLY COEXTENSIVELY ALONG THE ENTIRE LENGTH OF THE PLURALITY OF SUBSTATE BODIES.
 2. The method of claim 1 in which the substrate bodies are heated to an elevated temperature prior to vapor deposition.
 3. The method of claim 2 wherein said substrate bodies are heated by establishing an electrical discharge near said support bodies.
 4. The method of claim 1 including the step of forming an interface barrier on said substrate bodies prior to the raising of said bodies to an elevated temperature.
 5. The method of claim 4 including the step of establishing a glow discharge nEar said substrate bodies for forming an interface barrier on the surface of said bodies and for preheating said bodies prior to deposition of said material thereon.
 6. The method of claim 1 in which the crucibles are located outside the annular path of travel of the mandrels.
 7. The method of claim 1 in which the photoconductor comprises a material selected from the group consisting of vitreous selenium and vitreous selenium alloys.
 8. The method of claim 1 in which the material which is vapor deposited comprises a vitreous alloy of selenium and arsenic.
 9. The method of claim 1 in which the material which is vapor deposited comprises vitreous selenium alloyed with a material selected from the group consisting of arsenic, tellurium, thallium, antimony, bismuth and mixtures thereof. 